1. Field of the Invention
The present invention relates to a plasma processing method.
2. Description of the Related Art
In the case of a plasma process device such as the plasma etching device, upper and lower electrodes are opposed to each other in a plasma processing vessel. A matter to be processed is mounted on the top of the lower electrode. Etching gases are introduced into the plasma processing vessel and RF power is applied between the upper and the lower electrode. As a result, a plasma of the etching gases is excited. Chemical etching is applied to the matter by radicals created in the plasma while applying physical etching to the matter by ions created in the plasma and accelerated by electric field between the upper and the lower electrode.
In order to maintain good etching characteristics in this case, the lower electrode on which the matter is mounted is cooled by liquid He, for example, and the temperature of the matter is thus definitely controlled certain.
Further, the plasma processing vessel is being held under vacuum over a time period from the finish of the plasma etching process to the start of a next plasma etching process. The plasma processing vessel which has been thus held under vacuum to a certain extent is made ready for the next plasma etching process.
Even in the case of this plasma etching device, the etching gases are decomposed to a deposition when they are transformed to plasma. Just after the plasma etching process is finished and the process of placing the plasma processing vessel under vacuum is started, a flow of gas is created in the plasma processing vessel due to the evacuation of the vessel. The deposition is thus exhausted along this flow of gas from the plasma processing vessel.
After the plasma processing vessel has been evacuated to a certain extent, however, the flow of gas is ended. As a result, the deposition is left floating in the plasma processing vessel.
The deposition floating in the plasma processing vessel is gasified by that component which is cooled in the vessel. The deposition adheres to the component in this case. Particularly after the plasma process is finished and the matter is removed from the top of the lower electrode, most of the deposition floating in the plasma processing vessel adheres to the top of the lower electrode on which the matter to be processed is mounted, because the lower electrode is cooled to a predetermined temperature, as described above.
When the matter to be processed is mounted on the top of the lower electrode to which the deposition has adhered and the plasma etching process is applied to the matter under this state, the following problems are caused.
The deposition adhered makes the top of the lower electrode uneven. The distance between the matter which is mounted on the uneven top of the lower electrode and the upper electrode which is located above the matter and opposed thereto becomes different at various points on the face of the matter. As the result, etching characteristics or homogeneity of etching rate relative to the face of the matter is deteriorated accordingly.
Further, the deposition on the top of the lower electrode adheres to the underside of the matter. When the matter is to be processed at a next stage, therefore, the deposition on the underside of the matter acts as particles to thereby decrease the productivity of the matters processed.